1. Field of the Invention
The present invention generally relates to a fuel injection pump for an internal combustion engine.
2. Brief Description of the Related Art
Some prior art fuel injection systems include a fuel injection pump which uses a solenoid control valve as a spill valve and which controls fuel injection timing by spilling high-pressure fuel from a fuel pressurization chamber by opening and closing the spill valve, in which the spill fuel is refluxed to an intake gallery when fuel injection terminates and thereby the fuel supply rate to a plunger chamber for the next fuel intake stroke is secured to prevent a shortage in fuel supply to the plunger chamber. However, using this method of refluxing spill fuel to the intake gallery, a level difference in the fuel pressure within the intake gallery is created due to pulsation caused by the high-pressure spill fuel as illustrated by graph line 301 in FIG. 13. If the intake gallery pressure is high, the inner wall composing the intake gallery may be damaged; if the intake gallery pressure is low, a sufficient quantity of fuel can not be fed out into the plunger chamber. For these reasons, it is possible that fuel can not be supplied to the plunger chamber in a stable manner. Furthermore, even if the rotational pump speed rises, that is, even if the rotational engine speed rises, the level difference in the intake gallery pressure should preferably be within an allowable range as illustrated by graph line 302 in FIG. 14. However, since the level difference in the intake gallery pressure due to pulsation increases as the rotational engine speed increases as illustrated by the graph line 303 in FIG. 14, fuel injection characteristics falls particularly drastically at the high rotational engine speed range.
In order to solve the above problems, it is conceivable that a check valve is provided in a reflux passage through which fuel is refluxed from the spill valve to the fuel gallery and fuel flow is possible only in the direction from the intake gallery to the spill valve. In this arrangement, even if the pulsation is transmitted to the fuel within the intake gallery, when the fuel pressure is high, the check valve opens and the fuel flows to the spill valve, and when the fuel pressure is low, the check valve closes and the reflux of the fuel from the spill valve can be prevented, so that the fuel pressure within the intake gallery can be smoothed.
However, the conventional fuel injection pump provided with a check valve as described above cannot sufficiently flux the spill fuel to the intake gallery due to the check valve, and as a result, when the fuel is taken into the plunger chamber, the pressure within the intake gallery instantaneously falls and the fuel can not stably be supplied to the plunger chamber.